Kinetics of Ca2+ release evoked by photolysis of caged InsP3 in rat submandibular cells.
Quantitative time-resolved measurements of cytosolic Ca2+ release by photolysis of caged InsP3 have been made in single rat submandibular cells using patch clamp whole-cell recording to measure the Ca2+-activated Cl- and K+ currents. Photolytic release of InsP3 from caged InsP3 at 100 Joules caused transient inward (V(H) = 60 mV) and outward (V(H) = 0 mV) currents, which were nearly symmetric in their time course. The inward current was reduced when pipette Cl- concentration was decreased, and the outward current was suppressed by K+ channel blockers, indicating that they were carried by Cl- and K+, respectively. Intracellular pre-loading of the InsP3 receptor antagonist heparin or the Ca2+ chelator EGTA clearly prevented both inward and outward currents, indicating that activation of Ca2+-dependent Cl- and K+ currents underlies the inward and the outward currents. At low flash intensities, InsP3 caused Ca2+ release which normally activated the K+ and Cl- currents in a mono-transient manner. At higher intensities, however, InsP3 induced an additional delayed outward K+ current (I[K,(delay)]). I[K(delay)] was independent of the initial K+ current, independent of extracellular Ca2+, inhibited by TEA, and gradually prolongated by repeated flashes. The photolytic release of Ca2+ from caged Ca2+ did not mimic the I[K(delay)]. It is suggested that Ca2+ releases from the InsP3-sensitive pools in an InsP3 concentration-dependent manner. Low concentrations of InsP3 induce the transient Ca2+-dependent Cl- and K+ currents, which reflects the local Ca2+ release, whereas high concentrations of InsP3 induce a delayed Ca2+-dependent K+ current, which may reflect the Ca2+ wave propagation.
Takeo
T
T
Department of Physiology, Hirosaki University School of Medicine, Japan.
Suga
S
S
Wu
J
J
Dobashi
Y
Y
Kanno
T
T
Wakui
M
M
D000818:Animals; D002118:Calcium / Q000493:pharmacokinetics* / Q000528:radiation effects*; D018118:Chloride Channels / Q000187:drug effects / Q000528:radiation effects; D004305:Dose-Response Relationship, Drug; D015544:Inositol 1,4,5-Trisphosphate / Q000031:analogs & derivatives* / Q000378:metabolism / Q000528:radiation effects; D008297:Male; D008564:Membrane Potentials / Q000187:drug effects / Q000528:radiation effects; D018408:Patch-Clamp Techniques; D010782:Photolysis / Q000528:radiation effects*; D015221:Potassium Channels / Q000187:drug effects / Q000528:radiation effects; D051381:Rats; D017208:Rats, Wistar; D013363:Submandibular Gland / Q000166:cytology* / Q000378:metabolism* / Q000528:radiation effects
D018118:Chloride Channels; D015221:Potassium Channels; C061868:inositol 1,4,5-trisphosphate 1-(2-nitrophenyl)ethyl ester; D015544:Inositol 1,4,5-Trisphosphate; D002118:Calcium